A very fun tower defense game. I'm glad to see enlightened people that understood the mathematical beauty of hexagon. :) A very intuitive design, well-executed. You should be proud!
To make this game even better, I think you can consider making the UI better, as the game can be confusing at times. Make sure the visual hierarchy of the game is well maintained, meaning that there are visual guides to ensure the players receive the information you intended. Sometimes I missed the enemy simply because the game is too busy and the enemies blend in too well.
Great game. Nice job!